Downsizing the Channel Length of Vertical Organic Electrochemical Transistors

Abstract

Organic electrochemical transistors (OECTs) are promising building blocks for bioelectronic devices such as sensors and neural interfaces. While the majority of OECTs use simple planar geometry, there is interest in exploring how these devices operate with much shorter channels on the submicron scale. Here, we show a practical route toward the minimization of the channel length of the transistor using traditional photolithography, enabling large-scale utilization. We describe the fabrication of such transistors using two types of conducting polymers. First, commercial solution-processed poly(dioxyethylenethiophene):poly(styrene sulfonate), PEDOT:PSS. Next, we also exploit the short channel length to support easy in situ electropolymerization of poly(dioxyethylenethiophene):tetrabutyl ammonium hexafluorophosphate, PEDOT:PF 6 . Both variants show different promising features, leading the way in terms of transconductance (g m ), with the measured peak g m up to 68 mS for relatively thin (280 nm) channel layers on devices with the channel length of 350 nm and with widths of 50, 100, and 200 μm. This result suggests that the use of electropolymerized semiconductors, which can be easily customized, is viable with vertical geometry, as uniform and thin layers can be created. Spincoated PEDOT:PSS lags behind with the lower values of g m ; however, it excels in terms of the speed of the device and also has a comparably lower off current (300 nA), leading to unusually high on/off ratio, with values up to 8.6 × 10 4 . Our approach to vertical gap devices is simple, scalable, and can be extended to other applications where small electrochemical channels are desired.

Advanced Neuromorphic Applications Enabled by Synaptic Ion‐Gating Vertical Transistors

“…The need for new material architectures to shorten L without the use of high‐end techniques is the focus of recent breakthrough research. [ 37 , 40 , 94 ] Remarkable advancements have shown that incorporating electrolytes into vertical‐transistor architectures has numerous benefits. Among them, there is a decrease in power consumption and an increase in capacitance, both due to the dielectric based on the ultrathin EDL.…”

“…Adapted with permission. [ 94 ] Copyright 2023, Brodský et al. Published by American Chemical Society.…”

“…that comprised a spin‐coated poly(3,4‐ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) layer or an electropolymerized PEDOT:tetrabutyl‐ammonium‐hexafluorophosphate, (PEDOT:PF 6 ). [ 94 ] The device architecture is illustrated in Figure 3b.1 and is compatible with different OSC deposition processes for the investigation of new materials. Furthermore, the values of channel width ( W ), L , and nominal depth ( d ) can be adjusted by changing the thickness of the etched part of the silicon dioxide (SiO 2 ) layer.…”

“…successfully described a simple, scalable, and reliable method to obtain sub‐micrometer L for VOECTs, still maintaining good performance of the devices. [ 94 ]…”

Vertical organic electrochemical transistor platforms for efficient electropolymerization of thiophene based oligomers

“…14 The vertical OECT (vOECT) has been introduced as a variation on its planar counterpart, providing a useful geometry for facile reduction of the channel length, L, and additionally offering an advantageous platform for controlled electropolymerization. [15][16][17][18][19] This provides an opportunity to greatly expand the materials practically used in OECTs.…”